Wide-Line 1H NMR and DSC study of phase states of mesomorphic states of 4′-n-alkoxy-4-biphenylcarbonitrile mesogens (n = 3 and 7)

Abstract

4′-(Propyloxy)-4-cyanobiphenyl (3OCB) and 4′-(heptyloxy)-4-cyanobiphenyl (7OCB) have been studied in the temperature range 20–80°C by wide-line 1H NMR and DSC. The 1H NMR line shapes, half-widths, and second moments, as well as the relaxation characteristics of separate lines, are discussed. The DSC data are compared with the specific features of mesogenic transformations of these homologues and 1H NMR data. At certain temperatures depending on the composition of alkyl moieties, a dynamically disordered fraction of molecules appear in solid crystals. These molecules are involved in the thermotropic transitions of 3OCB to isotropic liquid and of 7OCB to nematic liquid crystal. The temperature ranges, stabilities, and other characteristics of the transitions of 3OCB to isotropic liquid and of 7OCB to nematic liquid crystal were determined.